22 



Heterotrypa robusta, sp. nov. 

 ' Plate II, Figures 7 and 8; Plate VL, Figure 2 



In the Streetsville member, several specimens of a coarse, ramose, smooth- 

 surfaced bryozoan were found, in which the zoarium varies from 12 to 15 mm. 

 in diameter. 



In tangential sections, the outstanding features of the species are the strong 

 inflection of walls by the acanthopores and the fact that most of these acantho- 

 pores are found between the angles of junction of the zooecial walls. They are 

 fairly numerous and of medium size. The zooecial tubes are small, 11 being 

 found in a space of two millimetres. The mesopores are not numerous and are 

 usually distributed evenly throughout the zoarium but are occasionally gathered 

 into maculae. 



In some parts of the tangential sections, distinct dark boundaries are seen 

 between the adjacent zooecial walls, while in other parts of the same sections no 

 evidence of a separation is visible, the walls being completely fused. Less 

 diversity is seen in the immature region where the walls are usually separate. 

 The variability in this respect leads to the conclusion that the fusion of the walls 

 is not a specific feature. A similar conclusion was reached with regard to other 

 species. In view of these observations the writer is inclined to question the value 

 of subdividing the trepostomatous bryozoans into Integrata and Amalgamata. 



In longitudinal sections the axial portion is seen to be comparatively small, 

 with a diameter not more than one-half that of the whole zoarium. In this 

 axial part the tubes run upward and outward with very thin and crenulated 

 walls. There are no diaphragms. On reaching the mature zone, the tubes 

 turn abruptly and run directly to the surface of the zoarium at the same time 

 becoming thick-walled. In this zone the walls are even and straight with 

 a slight suggestion of periodic thickening. Diaphragms are present with a 

 distance equalling one tube-diameter between them. Mesopores and acantho- 

 pores are seldom seen in longitudinal sections. 



Heterotrypa robusta resembles Heterotrypa microstigma, Cumings and 

 Galloway, of the Waynesville of Indiana, more than any other species, but the 

 average diameter of the ramose zoarium in the former is greater, and the minute, 

 raised, sub-solid maculae of H. microstigma are wanting. 



Locality. — Credit river, Streetsville. 



Nos. 12156, 12157, 12158, Royal Ontario Museum of Paleont 



HliTEROTRYPA SIMPLEX, Sp. 710V. 



Plate III, Figure 1 



This species is rather common in the Streetsville member where it forms 

 ramose or sub-ramose, smooth-surfaced zoaria, with an average diameter of 

 10 mm., as in //, simplex maculosa (Plate VII, Figure 10). 



In tangential sections, it is seen that the tubes are of a very uniform size and 

 rather small, twelve being found on the average in a distance of two millimetres. 

 Mesopores are entirely absent. Acanthopores are numerous, comparatively 

 small, and the regularity of their distribution is remarkable, one being found at 

 each angle of junction of the zooecial wall. Very rarely is a departure from 

 this occurrence found. 



In vertical sections, Heterotrypa simplex is almost identical with H. robusta 

 (Plate II, Figure 7). The structure is so similar, as thus revealed, that a 

 repetition of the description is unnecessary. 



